The quality of text or images written to or read from a markable medium such as paper by devices such as laser printers, xerographic printers, scanners, or ink jet printers is highly dependent on physical characteristics of the markable medium. The thickness, curl, mass, and stiffness of the medium being marked all affect the speed and accuracy with which a printer can transport a sheet of the markable medium, as well as affecting the accuracy with which text or images can be transferred to the markable medium. Generally, printers and copiers work well only with a limited range of paper and media types, with a sheet transport mechanism and an image transfer mechanism optimized for that range. In extreme cases, reasonable print quality is only possible with specially developed paper supplied by the manufacturer and maintained in pristine condition, unbent and at certain humidity levels to limit curling. Paper that is too thick, too thin, or even slightly curled may increase the risk of jamming or blocking the sheet transport mechanism.
Using various paper type settings, printers, copiers, and scanners might prevent errors in paper transport, and increase image quality without necessarily requiring specific manufacturer supplied papers. For example, a user could manually select a "thick paper" setting if thicker papers or thin cardboard stock is to be fed through the sheet transport mechanism. Spacing of pinch rollers and speed of transport would then be automatically adjusted to compensate for the increased paper thickness. Unfortunately, this solution requires extra effort from a user to identify the correct grade or type of paper being supplied to the printer. Further, this system is somewhat unwieldy if multiple paper types are intermixed, since the "thick paper" setting must be regularly enabled and disabled by the user as various paper types are fed through the sheet transport mechanism.
Thus, a need exists for an inexpensive paper handling system that automatically detects paper properties, and automatically adjusts settings of a sheet transport mechanism to optimize sheet handling speed, spacing, or other sheet transport characteristics based on the detected paper properties. Such a system would require minimal input from a user, and would automatically attempt to optimize its sheet handling characteristics to support use of a wide range of papers and paper conditions. Such a sheet handling system would allow for greater use of recyclable papers of differing quality and consistency, and could limit paper wastage by permitting use of lower quality or even slightly damaged papers, while still providing transport results comparable to those of pristine, newly manufactured papers.
Additionally, a need exists for a sheet handling system that provides information concerning paper properties to allow for optimizing adjustments in an image transfer mechanism. If paper properties such as heat capacity, thermal conductivity, dielectric constants, or resistance are known prior to image transfer, the image transfer mechanism can be suitably optimized to ensure the best possible text or image transfer. For example, if the thermal conductivity of the paper is known, the temperature of toner fusing module in a xerographic printer can be adjusted to optimally fix toner particles to paper without wasting energy through unneeded thermal heating of the paper, which may damage the paper.